Generally, a very highly accurate temperature control and high degree of cleanness are required in an exposure apparatus that is used in the manufacture of semiconductor circuits, particularly, for example, highly integrated super LSI (Large Scale Integration) and liquid crystal circuits. Accordingly, the entire exposure system (the main body of the exposure apparatus), which performs exposure, is arranged within a chamber. An air-conditioning room containing, for example, a heat exchanger, is provided for the exposure apparatus, and an air-conditioner supplies temperature-adjusted air into the chamber where the exposure system is installed. A ULPA (Ultra Low Penetration Air) filter, for example, is provided at the supply opening for the temperature-adjusted air, and air from which dust and dirt, for example, are removed, is supplied into the chamber, where the exposure system is installed. To accompany an improvement in the degree of integration of semiconductor circuits, it is necessary to remove extremely microscopic dust and dirt that float within the chamber, and the degree of microscopy in filters for the elimination of dust and dirt has been improved. Also, when using a chemical amplification type photoresist, a filter that removes chemical substances is provided in addition to the dust and dirt filter, in order to control deterioration in the performance of the photoresist.
Then, most of the air that is supplied to the chamber is brought back to the air-conditioning room and used for circulation.
A common projection exposure apparatus will be further explained with reference to FIG. 7. FIG. 7 shows an exposure system (main body of an exposure apparatus) 210 housed within a chamber 212 in which temperature-controlled air 214 circulates. A cooling device 216 which cools air that passes through the exposure system 210 and a heating device 218 which heats the cooled air to the proper temperature, are installed within the chamber 212. A temperature sensor 220 that detects the temperature of the air near the exposure system 210 is arranged alongside the exposure system 210. A temperature controller 222 controls the heating device 218 based on the temperature detected by the temperature sensor 220.
After the air temperature has been controlled by the heating device 218, the temperature-controlled air is sent towards the exposure system 210 by an air blower 224. A chemical substance filter 226 is arranged near the air blowing opening of the air blower 224 so that reactive chemical substances in the air are removed. A dust and dirt filter 228 is arranged in front of the chemical substance filter 226, and dust and dirt in the air are removed. Furthermore, an other chemical substance filter 230 is arranged within the chamber 212 in order to remove reactive chemical substances present in the outside air that is taken into the chamber 212.
A temperature control in each part of the exposure system that is higher in accuracy is required in order to comply with the need for further improvement in the accuracy of the exposure system. For this purpose, multiple blow-off openings are provided within the chamber. When many air blow-off openings are provided within the chamber, an increase in the air flow rate and an increase in pressure loss of the air flow occur and, therefore, it inevitably becomes necessary to increase the capacity of the air-conditioning equipment.
The increase in the air flow rate and the pressure loss within the chamber can be coped with by increasing the capacity of the air-conditioning equipment. On the other hand, vibrations that are generated from the air-conditioning equipment then become a problem.
More precisely, the level of vibrations generated by the air-conditioning equipment, which were previously small, did not cause many problems because the capacity of the air-conditioning equipment was previously small. However, as the capacity of the air-conditioning equipment increases, the vibrations generated also increase to the point where the vibrations reach a level that affects the accuracy of the exposure system. Of all the vibrations that are generated by the air-conditioning equipment, vibrations that are transmitted through the floor and mechanically coupled parts can be relatively easily coped with by providing a passive vibration isolating device such as a rubber pad, for example. However, an effective coping measure has not previously been discovered for reducing vibrations that are transmitted to the exposure system in the form of pressure waves of air, which is the medium for controlling the environment, that is, the so-called acoustic noise. A method in which vibrations are attenuated by forming a baffle within the flow path of air, a nd a method in which propagation is prevented by creating interference by dividing the flow path into two systems of different lengths, for example, can be considered. However, the equipment itself becomes oversized, and a large pressure loss occurs when such methods are used. Also, there is the inconvenience of not being able to sufficiently cover low frequency bands.
Moreover, a sirocco fan that uses forward curved vanes is generally mounted on the air blower of the exposure apparatus. A sirocco fan is used because it suits the pressure loss and the air flow rate that are generated in this type of device, noise audible to human hearing is low, and such an air blower is small in size and cheap in cost.
However, a sirocco fan has the characteristic of having a low noise audible to human hearing but having a loud noise, as physical noise that is actually generated, particularly at frequencies less than several hundred Hz. This noise at frequencies less than several hundred Hz is sound that is near the mechanical resonant frequency in an actual exposure system, for example. As a result, the sound pressure within the chamber fluctuates due to the noise that is generated from the air blower, and the mechanical resonance is excited.
When a sirocco fan is used as the air blower within an air-conditioning room of an exposure apparatus, it is known that the noise generated from the sirocco fan is noise near the mechanical resonant frequency of the exposure apparatus. A mechanical resonance is generated which drastically affects the alignment accuracy between the original plate (mask and reticle) and the substrate (for example, a wafer) that is to be processed within the exposure system, to a degree that cannot be ignored, and a proper exposure cannot be obtained.
Also, the known common exposure apparatus does not include a silencer for the purpose of reducing sounds near the mechanical resonant frequency of the exposure apparatus of less than several hundred Hz that are generated from the air blower.
Furthermore, noise from air blowers has become problematic in various kinds of devices, but noise audible to human hearing is considered problematic in all cases. Few studies have been made from the view point of industrial manufacturing devices that have a characteristic in which the mechanical resonance determines the performance of the device, as in an exposure apparatus for semiconductor integrated circuits, which apparatus is automatically operated with almost no inclusion of operators.